In recent years, much attention has been given to the components of warewashing detergents that treat and reduce the harmful effects of water hardness. Hardness ions are typically undesirable in conjunction with warewashing detergents since they interfere with the soil removal mechanism. Hardness ions typically comprise metal ions such as calcium, magnesium, iron, manganese, and other typically divalent or trivalent metal cations depending on the source of service water used in the warewashing environment.
Machine warewashing detergents are commonly highly alkaline, often providing wash water with a pH of 10.0 to 11.5, and are usually formulated by mixing or otherwise combining a variety of known organic and inorganic ingredients, such as alkaline detergent salts and alkaline condensed phosphates. Halogen-releasing agents also can be used in formulating warewashing detergents to provide stain removal and sanitization.
Condensed phosphates, such as sodium tripolyphosphate, have been used in the past as builders because of their detergency benefits and because of their water-treating properties. These benefits include soil dispersion, the sequestration of calcium, magnesium and other hardness ions, prevention of precipitation of calcium carbonate and magnesium hydroxide through a threshold effect, and chlorine stability. However, phosphates have been identified as contributing to water eutrophication, a process of excess algae growth in natural water. Many state governments have found it desirable to cause detergent makers to replace phosphates, particularly sodium tripolyphosphate, in warewashing and other detergents.
A significant problem has arisen in the search for a builder or builder system that is not a source of phosphate but provides all the detergency and water-treatment benefits of sodium tripolyphosphate. Many builders and combinations of builders have been evaluated in the past, but none have found commercial success in the warewash market. This is largely a result of the failure of these builders to provide one or more of the benefits of sodium tripolyphosphate.
It is recognized in the art that a threshold effect is desirable for use in a warewash machine. See U.S. Pat. No. 3,899,436. The threshold effect prevents precipitation of hard water metal ions at a concentration of ion in excess of the stoichiometric concentration of the sequestering agent. This is one reason why straight sequestering builders, such as ethylene diamine tetraacetic acid (EDTA) or zeolites, have not found commercial success. Detergents based on sodium tripolyphosphate sequester and rely on the threshold effect.
U.S. Pat. No. 4,579,676 discloses a liquid cleaning composition having a low phosphate content comprising an alkali metal hydroxide, a source of active chlorine, a water conditioning acrylic polymer, and a phosphinopolycarboxylic acid. The composition is particularly useful in cleaned-in-place equipment employed in the food processing industry.
U.S. Pat. No. 4,680,124 discloses a method of preventing the formation of calcium polyacrylate scale on industrial heat transfer surfaces such as boilers. The boiler water is treated with a water soluble phosphonate such as 1-hydroxyethylidene-1,1-diphosphonic acid. The warewashing environment of the present invention has a much higher pH than the boiler environment so scale is more difficult to control.
U.S. Pat. No. 4,539,144 discloses a machine dishwashing composition having a very low or zero phosphate content comprising an alkaline detergent material, a nonionic detergent surfactant, a water soluble calcium sequestering agent, and a hydrolyzed polymaleic anhydride.
U.S. Pat. No. 4,127,496 discloses a non-phosphate dishwasher detergent composition comprising an organic non-phosphate sequestering agent such as ethylenediamine tetraacetate or nitrilotriacetate, a nonionic detergent, a dry water-soluble anti-spotting agent, and non-phosphate alkaline and neutral builder salts.
U.S. Pat. No. 4,563,284, U.S. Pat. No. 4,581,145, U.K. Patent Application GB No. 2,137,185A, and Canadian Patent No. 1,117,395, all teach non-warewashing processes using a combination of monomer threshold agents and polymer dispersing agents to prevent calcium precipitation of the individual ingredients. While these systems obtain some value in either sequestration scale prevention or threshold performance, none provide the spectrum of properties needed in the replacement of condensed phosphates in machine warewashing.
A substantial need exists to provide a builder system for a warewashing detergent without intentionally added phosphate or polyphosphate that has all the detergency benefits of sodium tripolyphosphate or other condensed phosphate without its associated environmental harm.